We have an update now on a story NPR's been investigating for almost two years. This morning, federal prosecutors filed criminal charges in a 2010 coal mine explosion in West Virginia. Twenty-nine mine workers died in the blast at the Upper Big Branch mine. The charges reach into the management ranks of Massey Energy, the company that operated the mine. NPR's Howard Berkes joins us now for details.

Good morning, Howard.

HOWARD BERKES, BYLINE: Good morning, Renee.

MONTAGNE: Who exactly is charged, and what are they charged with?

BERKES: The criminal information that was filed today by the U.S. attorney in Charleston names Gary May, who worked at the Upper Big Branch coalmine as superintendant. He was the Massey Energy official in charge of that mine, and prosecutors say he conspired with other unnamed Massey officials to routinely violate mine safety law because they believe that following the law would hurt coal production.

MONTAGNE: OK, so this conspiracy, or this alleged conspiracy, how is it alleged to have led to that horrific explosion back in 2010?

BERKES: You know, prosecutors don't actually draw a direct connection between Gary May's behavior and that massive explosion, but they lay out a pattern of alleged behavior that put coal production before safety. They specifically accused May of falsifying the legally required records that identify safety problems and then lead to fixes. They say May thwarted surprise mine safety inspections with these coded warnings for miners underground. He allegedly manipulated the airflow underground to fool inspectors into thinking the mine had enough ventilation. And he's also charged with disabling a methane detector, the device that shuts down mining machines when two much explosive methane gas is present.

All this could get May five years in prison if he's convicted.

MONTAGNE: Now, May is the company official that you, in fact, first reported and documented had ordered the disabling of that methane detector. Is he the only one?

BERKES: He's the only one charged so far, and he was the senior official present that day when that incident happened in February of 2010. We had a number of witnesses who identified him as ordering the disabling of the methane monitor on the mining machine. The monitor was malfunctioning. It kept shutting the machine down, which it's supposed to do when there's too much methane present. Instead of just, you know, spending the two hours to retrieve and install a new monitor, May, according to the witnesses, ordered an electrician to disable it so that the mining could continue without the problematic methane monitor.

And, you know, that's an example of this production over safety pressure that put lives at risk in that mine.

MONTAGNE: And Howard, these charges. OK, so filed in a criminal information, which means that there was grand jury indictment. Is that significant?

BERKES: Yes, because prosecutors use a criminal information when they have a plea agreement and when the defendant is cooperating. Now, the charging documents don't say anything about that, and the prosecutors won't talk about it. But given the circumstances of these charges and the way they were filed, that's what's going on here.

You know, the mine superintendant, Gary May, is the highest-ranking mining company official to be charged in a mine disaster in the last 10 years, at least. And there are number of Massey Energy executives above him, including former CEO Don Blankenship. You know, Gary May is likely a stepping stone to these higher-level officials.